<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #bigImg{
            display: none;
        }
    </style>
</head>
<body>

<img id="smallImg" src="pre4.jpg" style="width: 100px;">
<img id="bigImg" src="pre4.jpg">
<script src="pics_big.js">

</script>
</body>
</html>